Date: Mon, 21 Apr 2003 09:24:49 -0400 From: Jake Burkholder <jake@locore.ca> To: Marcel Moolenaar <marcel@xcllnt.net> Cc: freebsd-hackers@freebsd.org Subject: Re: Is pmap_kextract() allowed to fault? Message-ID: <20030421132449.GA50754@locore.ca> In-Reply-To: <20030421055332.GA4680@dhcp01.pn.xcllnt.net> References: <20030421055332.GA4680@dhcp01.pn.xcllnt.net>
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Apparently, On Sun, Apr 20, 2003 at 10:53:32PM -0700, Marcel Moolenaar said words to the effect of; > Gang, > > On ia64 pmap_kextract() uses the tpa instruction which given a > virtual address returns the physical address based on the > translation registers and cache (ie TLB). This can fault when > there's currently no mapping for the virtual address. > > Since all other architectures have a non-faulting implementation > (AFAICT), I'm a bit worried that we might get into trouble on > ia64. I couldn't find anything about pmap_kextract(), so maybe > anybody can enlighten me: > > 1. Is pmap_kextract() allowed to fault? It depends what kind of fault. Will tpa fail if it causes a tlb fault and the page is not in the vhpt (or whatever the fault handler searches), or will it end up calling vm_fault and actually trying to fault in the page? pmap_extract/pmap_kextract are supposed to fail if the page is not mapped by the pmap. > 2. Is pmap_kextract() used often enough that using the cpu's TLB > is a possible performance speedup even if there are costly faults > that can sometimes happen? I doubt it. Jake
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